Various types of filters are known in the marketplace and in the patent literature.
Multiple-disk type filters generally include a housing in which the filter element within the housing is in the form of a stack of like, centrally-apertured, filter disks of substantially uniform thickness along their widths and having grooved side faces defining filtering channels between the adjacent disks in the stack. In some applications of such filters the outer face of the stack of filter disks constitutes the upstream side of the filter, in which case the fluid being filtered passes from the outer face to the inner face of the stack. In other applications of such filters, the inner face of the stack constitutes the upstream side of the filter, in which case the fluid being filtered passes from the inner to the outer face through the filter stack.
Multiple-disk type filters have a number of advantages over other known types of filters for example, the cylindrical-screen type filter. The multiple-disk filter has a larger capacity for removing and retaining dirt particles, since these may be retained also between the side faces of the disks in addition to being retained on the upstream surface as in the cylindrical-screen type filter. Another advantage in the multiple-disk filter is that it is not as easily ruptured as the screen type and therefore there is less danger that because of a malfunction, unfiltered water may pass through and clog sprinklers or other devices downstream of the filter. The latter advantage is particularly important in self-cleaning filters wherein the upstream face of the filter is cleaned by a cleaning nozzle which, in the case of a screen-type filter, may rupture the screen by particles becoming wedged between the cleaning nozzle and the filter screen.
Back-flushable filters of various types are well known in the art for a great variety of applications. A particularly successful type of backflushable filter employing filter disks is described and claimed in the following patents of applicant: U.S. Pat. Nos. 4,026,806; 4,042,504; 4,045,345; 4,271,018; 4,295,963.